when i slug a barrel, i find a mold that is fairly close to the size i need...for example, i used a 9mm (.356) mold to slug my .357. I did this by taking a cast bullet from the 9mm mold and hitting it with a hammer on the nose. It smashed it down a bit and in doing so made it a little fatter so I could slug my 357. The softer the lead the easier it is to slug the barrel. Good luck!